During the past year the laboratory has continued to investigate the regulation and function of the src family of tyrosine protein kinases (TPK) in a variety of human cellular systems. We have prepared numerous unique molecular and biochemical reagents for those studies and have analyzed in detail the expression of c-src, c-yes, fyn, Ick, hck, lyn and c-gar in hematopoietic cells. The results of these studies have defined expression of src family of tyrosine protein kinases in fresh human cells. Protein kinases of this gene family, such as the lck gene product, have been shown to be important for generation of IL-2 dependent proliferation signals and for activation signals following interaction between T-cells and antigen presenting cells. Using IL-2 dependent human T-cell lines we further characterized signal transduction pathway initiated by binding of IL,2 to the high affinity IL-2 receptor. We showed that IL,2 induced signal transduction in T cells is mediated by the lymphocyte tyrosine protein kinases p56(lck).